The human macrophage line U937 and human T lymphoblastoid leukemia line HSB2 have been rendered sensitive to hypoxanthine-aminopterin-thymidine (HAT) culture medium by treatment with 8-azaguanine. The cell lines have been fused to purified T lymphocytes that have been stimulated with concanavalin A, purified large granular lymphocytes, and purified monocytes. Hybridoma cell lines will be selected that retain the characteristics of the human peripheral blood cell but have been immortalized by the cell lines. These hybridomas will be screened for the production of various cytokines and will be studied in functional assays to see if they retain the effector function of the particular cell used for fusion.